1. Field of the Invention
This invention relates generally to structural forms used in the construction of trusses, columns, towers, spans, continuous planar decking surfaces, internal bracing of hollow spaces, etc. Such structural forms are used as elements of a wide variety of engineering and architectural macrostructures.
2. Description of the Prior Art
Man has long recognized the utility of interconnecting planar triangles to provide strength and rigidity to various structural forms. The common truss is perhaps the best know example of this concept. Trusses are plane structures composed of a series of adjoining triangles which are composed of straight members all lying in one plane. The members may be connected at their points of intersection by pins, gusset plates, welding, etc. The point of intersection is often referred to as a panel point or joint. Since rigidity of such trusses is secured by triangles which cannot be changed in form without changing the length of at least one side, it is generally assumed that loads applied at the panel points will product direct stress only. This would only be true, however, if the gravity axes of the members were to meet at the panel point and if the forces involved were being applied to members connected by means of frictionless pins. Actually, since the joints are rigid, bending stresses due to the deflection of the panel points are also developed. These stresses are commonly called secondary stresses. When a load is applied to a member between the panel points, it must distribute that load by beam action to the adjacent panel points. One of the many objects of this invention is to minimize strains resulting from these secondary stresses. Many other objects will become apparent in later parts of this disclosure.
It is also well-known that the strongest geometric structure known to man as well as found in nature, in terms of strength per weight unit and distribution of stresses, is the combination of six elements of equal length to form the edges of a regular tetrahedron. This is commonly known as a triangular pyramid--a solid having four vertices, six edges, and four equilateral triangular plane faces and in which three edges meet at each vertex. The strength of a lattice of this form is even exhibited at the atomic and molecular levels: diamond, the hardest known substance, exemplifies the tetrahedral crystalline lattice structure. Nature also employs the tetrahedral structure in the formation of the strongest and most stable chemico-physical bonds in molecules, compounds, and crystalline solids of carbon and silicon.
At the atomic and/or molecular levels, the natural formation of lattices of multiple tetrahedra is, without exception, external face-to-face, vertex-to-vertex connection (shown in FIG. 3). Any other connection would be a flaw in the lattice of these materials. The result of such tetrahedral configurations are macrostructures which show exceptional strength under compressive and tensile stresses, but are far weaker when subjected to torsional and flexural stress and buckling strains. It is also well known that man made structures, especially elongated members under compressive stress exhibit excessive strain unless these members are further supported in additional ways. The most common such support is provided by what is commonly called center-span lateral support, for which the overall supportable stress for a given structure increases dramatically.
In view of these observations, the methods and structures of this invention are built upon the permise that the basic strength of the RTL (as shown in FIG. 1) is unquestioned. It is axiomatic that, from a practical standpoint, such strength means support of applied stresses with minimum material in the several different ways that stresses may be applied. That is to say, that a structure may be strong in supporting a stress applied in one direction but weak to loads applied in another manner or direction. Thus, for example, common trusses such as shown in FIG. 2, would exhibit little strength if a bending moment were applied to it perpendicular to the two-dimensional plane of the truss. Similarly, nature's method of connecting tetrahedra, i.e., vertex-to-vertex (as shown in FIG. 3), shows little resistance to torsional stress and cannot be connected in continuous linear fashion, i.e., one-dimensional linear structures, or in planar, two-dimensional structures. Consequently, man-made approximations to such connections, RTL's assembled face-to-face, vertex-to-vertex, would exhibit little flexural, torsional, or buckling strength, nor would such assemblies lend themselves to the orthogonal structures of conventional design.